A New, Large Tornado Threat Looms Friday In Middle Of Nation. Also, Climate Change Worsening These Storms?

Areas in yellow, orange and red are in danger of severe
thunderstorms and tornadoes Friday. The areas in 
red are in particularly high danger. 

 After Friday's deadly tornadoes in Mississippi last Friday that killed 26 people, and sporadic severe weather daily since, a new, large threat is looming this coming Friday. 

Details are still sparse on the details of  how widespread and how violent the next round or severe weather will become, there's potential for some strong tornadoes.

The danger zone is also very unusually large. At this point a broad area centered on the central Mississippi Valley is under threat. 

Areas that could have severe weather and tornadoes extend from northern Iowa to central Louisiana, and from Missouri to Ohio. 

The culprit will be a strong storm system that will develop in the central Plains and pull a big plume of warm, very humid air northward all the way to the southern Great Lakes. 

The muggy, unstable air, combined with the spin in the atmosphere the large storm will help to provide, will trigger the severe weather.  The predicted storm is a classic set up for a big severe weather outbreak. 

That storm will eventually affect us here in Vermont. We son't have any tornadoes, but we will see rain, possibly starting out mixed with snow, a squirt of warm air, and possibly some downpours and some thunder. This could trigger some flooding if it gets toasty enough to melt a lot of snow and/or if it rains extra hard. 

A sharp cold front will plunge us briefly into near winter conditions Sunday before somewhat milder air arrives again.

Back to the tornadoes, after this week's system departs, another, similar storm seems poised to raise another tornado threat during the middle of next week, 

CLIMATE CHANGE

New research indicates climate change will increase the number of supercells hitting the United States overall, and more importantly shift the location of them further east, and extend the time of year they are more prevalent, reports the Associated Press.

The news is from a study by lead author Walker Ashley ad co-author Victor Gesini, meteorologists who study tornadoes and trends. 

A supercell thunderstorm looking north from Sheldon,
Vermont in May, 2018. Studies show supercells
will be getting more common in the eastern 
U.S. with climate change and somewhat less common
in the traditional "tornado alley" in the Great Plains. 

 Supercells are long-lasting, powerful thunderstorms with a very robust, rotating updraft of wind. Unlike garden variety thunderstorms, which typically blossom, then die within an hour or two, supercells often last for many hours over a long path. 

Not all supercells produce tornadoes. But if you're hit by a supercell, you're almost guaranteed to see large, damaging hail, destructive winds, or both. 

When supercells do produce tornadoes, some of those twisters can be extremely powerful, large and long-lasting. The tornado that carved a 59-path across Mississippi last week and destroyed towns like Rolling Fork was part of a supercell thunderstorm.

In general, supercells are increasing in number east of Interstate 35 and decreasing somewhat west of Interstate 35.

That interstate runs north/south through Austin and Dallas, Texas, into Oklahoma City and then curves somewhat northeastward to Kansas City before eventually continuing north through Iowa and eastern Minnesota. 

The research is consistent with what we've been already starting to see in recent years.

As the AP reports: "Cities that should see more supercells as warming worsens include Dallas-Fort Worth, Little Rock, Memphis, Jackson, Tupelo, Birmingham and Nashville, Ashley said 

The eastward shift also puts more people at risk because those areas are more densely populated than the traditional tornado alley of Kansas and Oklahoma, Ashley and Genuine said. The population coming under more risk is also poorer and more frequently lives in mobile or manufactured homes, which are more dangerous places in a tornado."

The mechanisms for this eastward trend in supercells and tornadoes is probably that the Southwest is getting hotter and drier, while the Gulf of Mexico is getting warmer, allowing hotter, unstable and more humid air to stream northward. 

The hotter air increases the strength of a "cap" that hinders supercell development, so under climate trends, the storms can't get going in the Plains like they used to. Meanwhile, the pressure builds under the cap until the wannabe storms near or pass the Mississippi River. Then they can explode into supercells. 

The bottom line is about a 7 percent increase in supercells nationwide and a 25 percent jump in the area and time of year they hit by the end of the century. 

By the way, we in Vermont occasionally see supercell thunderstorms. Though they only infrequently cause tornadoes in the Green Mountain State, they do cause wind damage and hail on average once or twice a year. The projections do show an increase in supercells here in Vermont, too. Though we will always have relatively few supercells, the fact that they might increase a little is a problem. 

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